Low Noise Microwaves for Testing Fundamental Physics

TL;DR

This study investigates the noise characteristics of cryogenically cooled microwave signals in sapphire resonators, demonstrating near-thermal noise limit performance that enhances precision in fundamental physics tests and quantum signal processing.

Contribution

It provides a detailed analysis of microwave noise suppression in cryogenic sapphire resonators, combining experimental measurements with Monte Carlo simulations to approach thermal noise limits.

Findings

Spectral densities of phase and amplitude fluctuations near thermal noise limit

Cryogenic resonators achieve noise levels suitable for precise physics tests

Potential applications in quantum signal processing

Abstract

We studied noise properties of microwave signals transmitted through the cryogenic resonator. The experiments were performed with the 11.342 GHz sapphire loaded cavity resonator cooled to 6.2 K. Based on the measured transmission coefficient of the cryogenic resonator we computed its noise suppression function. This was done via Monte-Carlo simulations some details of which are discussed in this Letter. Next, we measured technical fluctuations of a signal incident on the cryogenic resonator. Having processed these data with the previously computed noise filtering "template" we inferred noise spectra of the transmitted signal. We found that spectral densities of both phase and amplitude fluctuations of the transmitted signal were close to the thermal noise limit of -180 dB/Hz at Fourier frequencies F $\ge$ 10 kHz. Such thermal noise limited microwaves allow more precise tests of special relativity and could be useful at some stages of quantum signal processing.